Method of and apparatus for molding



May 3, 1949. 1 l. P. RODMAN, vJR 2,469,130

METHOD OF AND APPARATUS FOR MOLDINGAl Filed oct. 17', 1945 -T/ .22 :i 2z

lNvENToR Poo/AN JP.

ORNEY Patented May 3, 1949 METHOD OF AND APPARATUS FOR MOLDING Isaac P. Rodman, Jr., West Orange, N. J., assignor to Celluplastic Corporation, Newark, N. J., a corporation of New Jersey Application (ictober 17, 1945, Serial No. 622,710

10 Claims.

This invention is directed to the molding of plastic materials by a novel method and apparatus.

In methods heretofore proposed in this art for molding tubular objects, it has been necessary to use preforms and split molds, and special nonautomatic equipment. By means of my invention objects may be molded in fully automatic machines. It will be apparent to those skilled in this art that the attainment of said objectives by the method and apparatus of my invention, permitting the use of fully automatic machines, represents a distinct and valuable advance in the art.

The foregoing and other advantageous bjects, which will appear from the description hereinafter, are accomplished by a method and apparatus illustrated in the accompanying drawings, in which:

Fig. 1 is a vertical, transverse sectional view of a mold embodying my invention showing the rst step of my process, which consists in flowing the plastic material within a sleeve and around a mandrel disposed within the mold,

Fig. 2 is a similar View, showing the position of the parts in the second step of my process, that is, on retraction of the sleeve from the cavity,

Fig. 3 is a similar View, showing the position of the parts in the third step of my process, in which the blank of plastic material is expanded against the walls of the cavity,

Fig. 4 shows the position of the parts in the fourth step of my process, in which the apparatus on which the completed article is positioned, together with the completed article, is withdrawn from the mold cavity, and

Fig. 5 is a fragmentary enlarged sectional view of the mandrel check valve taken at line 5 5 of Fig. 2.

As shown in Fig. 1 of the drawings, the first step of the process of my invention consists in owing a blank Ill of plastic material in the form of a generally closed tube within a retractable sleeve I3 (which at one end abuts the cavity i8 and closes the same) around the mandrel I I and on the retractable plunger 2S. The plunger 25 is disposed within and closes the other end of the sleeve adjacent the end of the mandrel, the latter containing a check valve I2. The sleeve I3 is telescopically arranged with respect to the mandrel to define therewith a tubular chamber to receive plastic material. The parts referred to are disposed within the cavity block I4, the plastic material being introduced in any desired or conventional manner, as through the runner I5 and gate it terminating in the blank I0. The cavity block Ill may be provided with any desired or convenient heat exchange means, such as conventionally indicated at I'I in Fig. 1. Additional or other heat exchangev means such as indicated at Il' of Fig. 1 may be provided throughout the apparatus as desired. The heat exchange means may, as shown at Il, il', be a Water system used for heating or cooling purposes, depending on the plastic material used, and on the cycle of operation and other factors well known in this art. It will be Aunderstood that the mold may be a multiple cavity mold comprising a group of units such as that shown in Fig. l, arranged in a manner which will be obvious to those skilled in this art; likewise the mechanism yfor feeding plastic material to the runner l5, as through a sprue medially arranged with respect to the units of the machine, may be any conventional or desired means such as are well known in this art. The cavity block I4 is shown as being of an injection molding type; any other method 0f supplying the material to the mold suited for use with the apparatus and process described herein may be used in carrying outthe invention, within the purview of the invention.

The blank Ill is initially formed as shownin Fig. 1 by injection or otherwise flowing the plastic material through the runner I5 in a freeflowing, near-liquid mass; the blank I0 if of a thermoplastic material is cooled suliciently to attain stability of form.

When the blank has attained stability of form, that is,lwhen it possesses sufficient shear strength so that the outside walls of the blank will not tend to tear on withdrawal of the sleeve I3, the latter is Withdrawn from the cavity I8 as by means of bar 2l to a position substantially flush with the upper edge 2!! of the reduced portion 2l of the bottom force part i9 which is adapted to be received within the cavity block Ill to close the bottom thereof. vThe stability of form of the blank Ii! onl withdrawal of sleeve I3 from the cavity ireferred to above is that state at which the blank is in a semiplastic form, viz: approximately the temperature at which plastic material leaves an extrusion-die, which for the more cornmon forms of injection ymolding material ranges from 250 F. to 350 F. at the date of filing this application. l

The third step of my process consists of the introduction of an expansion medium into the blank l0, through the mandrel II, as for example the introduction of compressed air or other gas or expansion .means from an external source 22.- The checkvalve I2 normally closes.

The check valve I2 may be pressure urged toV penetrate slightly into thegplastcrvmaterial'fadjacent the end of mandrel II, or the plunger 26 may be slightly withdrawnf'awayfrom' theyva'lve end of the mandrel to facilitate the"'discharge 'of the expansion medium through the valve end of the mandrel. The cavityiblockifl may-then be temperature controlled by heat exchangev system II to harden the completed object' 25 as 'is common in this art.

vrThe* fourth "stepvoff my invention isf illustrated in`-Fig.y -`4 and' consists fof tlieffejectionoff thev completed 'objectf2li-l from:x thef'mold 'by'f withdrawing thev sleeve I3,l plun'g'ex-"26'aridE bottom forcepart I9 from the"moldrbycontinuingthe air pressure through tlie'niandrel,objectl25` will be broken from the .gate I6 \andwill"move v:out of cavity I8 on the parts t3," I9 land 2E. lAny suitable orsup- .plementaryf'expedientimayberesorted to in aid of. theremovalofobect'Z 5.

The sleeve I3 may "rfbe tof 'sany desired cross section, as -`mayziaiso'tl'ieLfrnzaridrel r I I n the latter may wbe c of such :outline "as "desired to `regulate the: vvall'v 'thicknesses cf'*'thef"inished'"article; i the mandrel "should Lbe -nowhere v"larger"lv than at the neck'of the bottle;sofastoipermitmwitlidrawal of the latter.

The four. steps above referred to zare 'the Aonly ones` necessary intl'oarrying out the "moldin'g'operationspursuant to myinvention. KThe mold I4" then'maybe openedfinithe usual' manner 'on thepartlnaline. 'thereoffar enough* fori the runners Iliandsprue to'bei'e'cted.

".The sleeve I3may"bey-gffany:desiredzuniform cross-section. "Themandrlicheckva'lve may be f of any desired construction "which normally closes i the 'mandrel @responsive 1 to xincter'nal 'pressure and :permits opening the' valve L responsive tolinternal pressure 'The-precisepressure re- Nquired; toppen the'vlveiis.readilyfdetermined according tothe respective dimensionsof'theparts and all other,v pertinent;.factors. .Jnl'ig T5 there is .'i1lustrated.-,one;of .rma'ny .possible "forms of i the cheek valve '2 .wherein the seat 22.4 .thereof is s'hown.'forzne'd.on'a. 'meniber :secured iriteriorly :of .the .endaof '..the mandrel LI I. 'IIn Lthe 'steps of my processJillustrateddniFigs.il.and'ZLthe external pressure of rthe .plasticsmaterial .of blank IJforces the yvalve :.I2to .a losedposition. `.The mandrel valve l I2 is .displaced .from `its k.se-at 24 when l air ,pressure .is introduced with '.the .mandrei .in the third ,and fourth-.steps of my ,process '(seelE'igs. .3. andffi).

',The `broad .principles of rthe. invention are .re ferred to aabove. .It .will be .apparent to those skilled Ain the art .that ,many `rconventional `.expedientsisuch as rotatable .bushings to V,forman externally threaded rneek, er1-the Y.rotating of a threaded mandrel for an internally threaded neckziinrtlrefnished article may be employed in '.carryingfout the invention .Thefobjectsiformedby .the method fand apparatus eabove :fset forth l`.do-not ahfave :a: parting line such :fas i they *would have if .fnrm'ed 1in nvthe :split molds proposed hereto'forefor mldingbottles.

4 The carrying out of my invention does not require costly special equipment; conventional molding machines may be used, provided with the apparatus and operated in accordance with the method of my invention. The invention permits the molding of objects on fast cycles in completely automatic multiple cavity molding machines with all conditionsicontrolled.

"Any suitable means 'generally vdesignated in Fig, l as members 28 and 29 engaging members vl2li and I9 respectively to reciprocate the latter 4inV unison 'or-independently relatively to member I4 may be provided; the members I9, I3 and 26 ymay: be retracted'orreciprocated relative to the .member I4 selectively or in unison as desired in carrying'outmy invention as above set forth.

Havingthus'fdescribed my invention, what I claim as new and desire to secure by Letters Patent', is:

1. The method of molding plastic objects which consists -in liiovv'ing plastic material Within a sleeve and around afmandrel and ona plunger positioned Within a mold cavity, a bottomvforce part in whichV said-sleeve fis "slidably disposed, said force-part defining' the bottom'ofsaid cavity, to define a plastic blank, displacing the sleeve from the mold cavity, and-introducing an expansion medium through the mandrel into the blanlexpanding the latter aga-instthe'vvalls of thejcavity to define the object to be molded; andv Withdrawing the sleeve, force partfand'plungervvhile'continung 'the introduction'ofthe expansion medium, thus removing said bjectirom't'he-mold cavity.

2. In` an vvapparatus for molding plastic objects ina mold having afcavityya bottom part and plunger `received Within-thelower lendof the cavity to `close the lsa`rr'1e,'a sleeve "sli'dably Aarranged in said bottom part, meansto" reciprocate said sleeve, plunger and'bottom part relativeto saidl cavity, a "mandrel"4 positioned in said mold and projectingme'dially. lntjo said sleeve when the latteris positioned inthe mold 'means to supply a fluid.' to'jsaid mandrel, whereby plastic material may be'owed 'into said l,sleeve varound themandrel to deneaplasti'c blank, andthe sleevemay be withdrawn'fromthe cavity, :and the .fluid may be introduced from said mandrel into the blank to"eX'pa`nd the "blank againstlthe Walls 'of' the Vcavityvvl'len the sleeveis withdrawn from' the'cavit'y todene'the obje'ct'to be molded.

3. In an apparatus for molding plastic 'objects in a mold'having a'ca'vity, a bottom part and plunger reoeive'd'with'in the lovver end of the cavity to 'close the -same, `a sleeve 'slidablyarranged in saidV bottom part, means to 'reciprocate said sleeve, plunger vand ".bottor'n4 part 'relative to said cavity, a mandrel positioned in said mold and projecting mediallyi'nt'o'said sleeve'when the latter is positioned inthe mold, `vvhereby plastic material may be 'flo'wed '.intolsai'd lsleve around the 4mandrel to definela plastic blank, 'and the sleeve maybe Withdravv'nfrom the cavity.

4. .The method of forming hollow articles from organicplastic material fin a 'mold comprising a closed mold cavity 4tlie'lower end of vsaid'cavity being vdeiineclby a force npartand a retractable sleeve slidably disposed 1in said'ior'cepart, a tu bular mandrel extending into the lsleeve and spaced therefrom to Akform -a closed initial blankforming space, which -metho'd `Acom-prises V-ilovving plastic material intovthe -initial blank-forming space, until 'the blank-formingl space isiilled with the plastic material, :thereby mol`ding -v a starting blankf enclosing thertubular mandrel, allovvinglthe plastic blank to remain in the molding space until the said plastic material becomes partly -selfsustaining, retracting the retractable sleeve from the still plastic blank while leaving the blank still surrounding the mandrel and expanding the resulting blank by applying a uid pressure medium to the interior of the blank through the tubular mandrel to effect such expansion while holding the blank against longitudinal movement relative to the mold cavity as it is expanded therein, and thereafter expelling the resulting molded article from the mold cavity by further withdrawing the sleeve and force part completely from the mold cavity while continuing introduction of the pressure medium into the molded article.

5. The method of forming hollow articles from plastic materials in a mold comprising a closed mold cavity, the lower end of said cavity being dened by a force part and a retractable sleeve sliclably disposed in said force part forming a closure for said cavity, and a tubular mandrel extending into the sleeve and spaced therefrom to form an initial blank-forming space, which method comprises injecting a stream of the plastic material in iuid condition into the blankforming space until the space is filled with the plastic material to produce a starting blank, allowing the resulting initial, plastic blank to become self-sustaining but still in plastic condition, enlarging the initial blank-forming space after the initial starting blank has become self-sustaining into a mold cavity, expanding the initial blank into final shape by admitting a fluid pressure medium into the said blank thereby expanding the blank laterally into finished shape, and then withdrawing the sleeve and force part and ejecting the expanded article from the mold cavity by continued admission of the fluid pressure medium.

6. The method of forming hollow articles from plastic material which comprises providing a closed mold having a cavity therein of an internal configuration corresponding to the shape of the article to be molded, providing in the said mold cavity means dening a closed, substantially cylindrical die space, introducing uid plastic material to be molded into the cylindrical die space, until the space is lled with the material, allowing the plastic material to become self-sustaining in the said space while maintaining the said space constant in its dimensions, thereby forming a substantially cylindrical, but plastic starting blank, removing the cylindrical die space means die parts from around the starting blank while maintaining the starting blank in initial position, expanding the blank laterally While restraining the blank longitudinally by introducing a iiuid medium into the blank until the expanded blank fills the mold cavity, restraining a portion of the cylindrical blank at an end thereof while expanding the remaining portion of the blank into engagement with the sides of the mold cavity, and after expansion of the article in the mold cavity, effecting release of the resulting expanded article from the mold cavity by opening the bottom portion of the mold while continuing introduction of the fluid medium into the expanded article under sufficient pressure to effect ejection of the expanded article from the mold cavity.

'7. An apparatus for molding articles composed of plastic materials by injection molding, which comprises, in combination, an injection mold provided With a mold cavity having a configuration corresponding to the article to be molded, a tubular mandrel extending into the mold cavity,

a retractable sleeve extending longitudinally axially through the mold cavity and enclosing the tubular mandrel in spaced relation thereto, the sleeve defining an initial forming die around the mandrel, a plunger in the sleeve, a reciprocable force part forming an end closure for the mold cavity and surrounding the retractable sleeve, means for injecting plastic material into the initial forming die for producing an expansible initial blank of the material, means for retracting the sleeve from around the mandrel and the initial blank of plastic material and means for introducing -compressed expansion fluid through the mandrel into the blank for expanding the blank laterally into engagement with the walls of the mold cavity, the said force part being adapted to be withdrawn from the cavity during continued application of the pressure iiuid into the expanded shape to thereby eject the expanded shape from the mold cavity.

8. An apparatus for molding articles composed of plastic materials by molding, which comprises, in combination, a molding block having a mold cavity therein, the walls of which have a contour defining the shape of a finished molded article, a retractable sleeve having an end abutting the mold cavity and closing the same, a tubular mandrel extending through the mold block into the tubular sleeve, a retractable plunger in the sleeve forming a closure for the sleeve adjacent the end of the mandrel, the sleeve being telescopically arranged with respect to the mandrel to define therewith a tubular chamber to receive plastic material, means for supplying fluid plastic material to the tubular chamber, means for telescoping the sleeve relative to the mandrel for withdrawing the sleeve from around an initially molded blank of the plastic material, means for introducing an expansion medium through the tubular mandrel into the molded blank for laterally expanding the blank against the walls of the mold cavity, means including a bottom force part for the mold cavity and the said end of the sleeve for restraining the blank from longitudinal movement during expansion thereof, and means for withdrawing the force part, plunger and sleeve entirely from the mold cavity, whereby, upon continued application of expansion medium into the expanded article, the said article is ejected from the mold onto the force part, sleeve and plunger and thereby released from the mold.

9. An apparatus for molding articles composed of plastic materials by molding, which comprises, in combination, a mold comprising a mold block provided with a mold cavity having a configuration corresponding to the article to be molded, a tubular mandrel extending into the mold cavity, and dei-'ming with the mold block a cylindrical space adapted to form the upper end of the article to be molded, a retractable sleeve extending longitudinally axially through the mold cavity, and enclosing the tubular mandrel in spaced relation thereto, the mold cavity tapering at its inner end to the cylindrical space to define a tapering portion end of the molded article, the said sleeve when in closed position defining an initial forming die around the mandrel, a plunger in the sleeve, movable relative thereto, a reciprocable force part forming an end closure for the mold cavity and surrounding the retractable sleeve, means for injecting plastic material into the forming die for producing an expansible initial blank of the material, means for retracting the sleeve from around the mandrel and the initial blank of plastic material, and means for introducing: compressed. expansion fluid; through. the' mandrel into thev blank ,for *expandingV thev blank: laterallyr into engagement-'withthe Walls ofthe moldca'vity, the saidforcepart restraining the' blank. against` longitudinal movement during lateral expansion thereof, whereby, that portion of `the blank in the cylindrical space between the mandrelsandA the mold blank is restrained against. expansion toform the molded article,` and vmeans-` for: withdrawing the force partl completely from the mold cavity after lateral expansion ofv the blank, whereby, upon continued application of the compressed expansion fluid, the molded article isrel'eased'from the mold.

10. The method' of molding plastic objects.

whichA consistsin flowing plastic material within'V asleeve-and around a mandrel and on axplunger positioned within'a mold cavity the lower endof saideavity being 'defined by a force part in whichY the sleeve is slidably disposed, to dene'aplastic y20,: Number.

blank; displacing the .sleeve from the mold cavity longitudinally. axially thereof,v introducing anexapansion medium through theK mandrel into thel blank, expanding the latter againstthe .walls of:v

thecavity to'dene the object to loe-molded, and

REFERENCES CITED T1'ie following references yareof' record in' thele of this patent:

UNITED STATES. PATENTS Number Name Y Date 484,131- Att'erburyY Oct. 1'1`, 1892 598,224' Hys Feb. 1, 1898 2ff31688` Hobson v Oct. 12,` 1943 FOREIGN `PATENTS Country Datel 327,225 Francef Mar. 18, 1903` OTHER.l REFERENCES ModernzBlastics; hyiieoD. Felton; May; 1941,'` 18+I. Digxfpagest'lf and 102) 

